APPENDIX - On the dehydration of lactic acid in near- and supercritical water

Estimation of the errors from the HPLC analyses

Overlapping of the peaks in the chromatograms is a source of errors in the calculation of the concentration of the analyzed substances. The use of different graphical integration methods for calculating peak areas lead to different results for the concentrations of the substances.

The basic methods used are represented in Figure 10-1.

Figure 10-1 Different methods used for the graphical integration of overlapping peaks for the calculation of the concentration of the respective substances.

The overlapping in analyses always had a similar configuration to that seen in Figure 10-1 and involved a large peak preceded by a relatively small one. The area corresponding to the real concentration at least in the case of the larger peak should be in a range limited by the smallest and largest areas marked with red on Figure 10-1.

The results of the graphical integration using the methods mentioned in Figure 10-1 from experiments carried out at 385 °C are given in Table 10-1. The variance for samples (s²) is calculated using (10-1). At 0 seconds residence time the concentration of lactic acid is that of the feed. It was set at 0.1 mol l^-1 and was considered free of graphical integration errors since no overlapping was present in the analysis of the pure lactic acid solution.

² ²

1 ( )

1 ₌

= −

−

∑

ⁿ i i

s x x

n (10-1)

with the mean value =

∑

⁼ⁿ¹ i i

x n . The methods represented in Figure 10-1 yield area intervals that include the value corresponding to the real concentration, at least in the case of the first peak which in all encountered overlapping cases is the larger.

Table 10-1 Graphical integration of data at 385 °C and residence times between 0 and 300 s.

Feed: Lactic acid 0.1 mol l^-1; Pressure: 350 bar; Temperature: 385 °C R.t. Conc. Lac Conc.

Acr Conc. Ald Conc. Lac Conc. Acr Conc. Ald /s /mol l^-1 /mol l^-1 /mol l^-1 m.v. m.v. m.v.

0 0 0 0.1 0.1 0 0 0 0 0

0.08398 0.00755 0.00922 0.08359 0.00739 0.0078 0.08447 0.00764 0.0078 16

0.08391 0.00755 0.00911

0.083988 0.007533 0.008483 1.32E-07 1.083E-08 6.231E-07

0.07149 0.01259 0.01507 0.07113 0.01234 0.01356 0.072 0.01234 0.0136 32

0.07175 0.01204 0.0136

0.0715925 0.012328 0.013958 1.38E-07 5.063E-08 5.504E-07

0.05391 0.01929 0.0237 0.05387 0.01929 0.02297 0.05353 0.01888 0.02143 65

0.05353 0.01959 0.02143

0.05371 0.019263 0.022383 4.35E-08 8.502E-08 1.298E-06

0.04535 0.02192 0.02739 0.0453 0.02192 0.02637 0.045 0.02147 0.02493 100

0.04603 0.02227 0.02546

0.04542 0.021895 0.026038 1.89E-07 1.075E-07 1.167E-06

0.02829 0.02453 0.03191 0.02826 0.02453 0.03273 0.02785 0.02397 0.02905 200

0.02827 0.02498 0.02818

0.028168 0.024503 0.030468 4.5E-08 1.71E-07 4.814E-06

0.02129 0.02207 0.03174 0.02092 0.02152 0.02961 0.02135 0.02256 0.03101 300

0.02126 0.02246 0.03101

0.021205 0.022153 0.030843 3.75E-08 2.225E-07 7.936E-07

The errors from quantifying the concentrations also influence indirect quantities such as selectivities. For estimating the indirect errors arising from this propagation of errors, a deviation of 2 s (two times the standard deviation of the mean) from the mean will be considered. A confidence interval of ±2 s gives a level of certainty of 95 % for a normal distribution for the errors.

The mean selectivities towards products determined from the graphical integration can be written as:

Acr ^Acr 0,Lac Lac

Sel c 100

c c

= ⋅

− (10-2)

Ald ^Ald 0,Lac Lac

Sel c 100

c c

= ⋅

− (10-3)

sLac s²_Acr s²_Ald

c^Acr mean concentration of acetaldehyde /mol l^-1 c^Ald mean concentration of acetaldehyde /mol l^-1 c^Lac mean concentration of lactic acid /mol l^-1 c^0,Lac initial concentration of lactic acid /mol l^-1

The mean values of the concentrations of lactic acid, acrylic acid and acetaldehyde are subject to errors from graphical integration. For the initial concentration of lactic acid, these errors are negligible. Thus, the two selectivities can be written as functions ofcAcr, cAld andcLac:

Sel^Acr = f¹(c^Acr, c^Lac) (10-4) Sel^Ald = f²(c^Ald, c^Lac) (10-5) For each substance an error is set in accordance with the 95 % level of certainty:

ε^Acr =2s^Acr (10-6) ε^Ald ⁼2s^Ald (10-7) ε^Lac =2s^Ald (10-8)

with s_Acr, s_Ald, s_Lac the standard deviations from the mean of the respective substances.

The functions defined in (10-4) and (10-5) can be expanded through Talyor series around the points (cAcr, cLac)and (cAld, cLac)using (10-6) to (10-8) in the following manner:

p q p+q

Acr Lac

Acr Lac Acr Lac Acr Lac

1 Acr Lac 1 p q 1

p=0 q=0 Acr Lac

(c + , c + ) (c , c ) + (c , c )

p!q! c c

f ε ε = f ^∞ ^∞ ε ε ⋅ ^∂ f

∂ ∂

∑ ∑

(10-9)

p q p+q

Ald Lac

Ald Lac Ald Lac Ald Lac

2 Ald Lac 2 p q 2

p=0 q=0 Ald Lac

(c + , c + ) (c , c ) + (c , c )

p!q! c c

f ε ε ⁼ f ^∞ ^∞ ε ε ^⋅ ^∂ f

∂ ∂

∑ ∑

(10-10)

For the purposes concerning the errors, the expansions can be limited to first order derivatives and first degree terms for the errors (provided that the errors are sufficiently small):

1 Acr Acr Lac Lac 1 Acr Lac Acr ¹ Lac ¹

Acr Lac

(c + , c + ) (c , c ) + +

c c

f f

f ε ε = f ε ^∂ ε ^∂

∂ ∂ (10-11)

2 Ald Ald Lac Lac 2 Ald Lac Ald ² Lac ²

Ald Lac

(c + , c + ) (c , c ) + +

c c

f f

f ε ε = f ε ^∂ ε ^∂

∂ ∂ (10-12) By derivating using (10-2) and (10-3) and regrouping:

1 Acr Acr Lac Lac 1 Acr Lac ^Acr ^Acr ^Lac 2

Lac Lac

0,Lac 0,Lac

(c + , c + ) (c , c ) + c

c c (c c )

f ε ε − f = ε ^⋅ε

− − (10-13)

2 Ald Ald Lac Lac 2 Ald Lac ^Ald ^Ald ^Lac 2

Lac Lac

0,Lac 0,Lac

(c + , c + ) (c , c ) + c

c c (c c )

f ε ε −f = ε ^⋅ε

− − (10-14)

One can define

SelAcr

ε ^andε_Sel_Acr^as:

Acr

Acr Acr Lac

Acr Lac Acr Lac

1 Acr Lac 1

Sel 2

Lac Lac

0,Lac 0,Lac

(c + , c + ) (c , c ) + c

c c (c c )

f f ε ε

ε = ε ε − = ^⋅

− − (10-15)

Ald

Ald Ald Lac

Ald Lac Ald Lac

2 Ald Lac 2

Sel 2

Lac Lac

0,Lac 0,Lac

(c + , c + ) (c , c ) + c

c c (c c )

f f ε ε

ε = ε ε − = ^⋅

− − (10-16)

By replacing the errors from (10-6) to (10-8) one obtains:

Acr

Acr Acr Lac

Sel 2

Lac Lac

0,Lac 0,Lac

2s c 2s

c c + (c c )

ε = ^⋅

− − (10-17)

Ald

Ald Ald Lac

Sel 2

Lac Lac

0,Lac 0,Lac

2s c 2s

c c + (c c )

ε = ^⋅

− − (10-18) Thus, an estimate for the errors of selectivities has been obtained based on the mean

concentrations and errors of lactic acid, acrylic acid and acetaldehyde. The respective results are to be found in Table 10-2.

Table 10-2 Estimation of errors for selectivities at 385 °C, 350 bars, residence times from 16 to 300 seconds and 0.1 M lactic acid feed.

R.t. / s ε_Acr /% ε_Ald /% ε_Lac /% /% /%

16 2.76 18.61 0.87 47 ±7 53 ±23 7.31 23.15

32 3.65 10.63 1.04 43 ±6 49 ±13 6.27 13.25

65 3.03 10.18 0.78 42 ±4 48 ±11 3.93 11.08

100 2.99 8.30 1.92 40 ±5 48 ±10 4.59 9.89

200 3.38 14.40 1.51 34 ±4 42 ±15 3.97 14.99

300 4.26 5.78 1.83 28 ±5 39 ±6 4.75 6.27

SelAcr /% SelAld /%

SelAcr

ε ε

SelAld

Results

Influence of the residence time (reaction time)

Feed: Lactic acid 0.1 mol l^-1; Pressure: 350 bar T

/°C R.t.

/s Conv.

Conc.

Lac /mol l^-1

Conc.

Ald /mol l^-1

Sel.

Ald /%

Conc.

Acr /mol l^-1

Sel.

Acr /%

18.0 4.17 0.0964 0.0025 59.19 2.47 0.0021 49.58 2.07 32.2 7.53 0.0930 0.0042 55.05 4.15 0.0039 51.21 3.86 50.0 12.64 0.0879 0.0074 58.40 7.38 0.0058 45.27 5.72 65.3 15.00 0.0855 0.0086 56.92 8.54 0.0073 48.59 7.29 100.1 22.35 0.0781 0.0116 51.55 11.52 0.0112 49.76 11.12 101.2 23.76 0.0767 0.0124 51.85 12.32 0.0105 43.87 10.42 150.8 30.00 0.0704 0.0150 49.85 14.95 0.0126 41.86 12.56 190.5 33.11 0.0673 0.0140 42.09 13.93 0.0160 48.17 15.95 253.5 40.02 0.0603 0.0198 49.24 19.71 0.0158 39.30 15.73 305.7 40.90 0.0595 0.0168 40.85 16.71 0.0189 45.87 18.76 506.9 50.99 0.0459 0.0204 42.86 21.85 0.0205 42.96 21.91 350

936.5 64.25 0.0358 0.0186 28.95 18.60 0.0204 31.66 20.34

16.6 15.92 0.0840 0.0085 53.33 8.49 0.0075 47.36 7.54 20.2 23.06 0.0775 0.0118 50.65 11.68 0.0090 38.92 8.98 31.9 28.33 0.0716 0.0140 49.32 13.97 0.0126 44.51 12.61 64.6 46.23 0.0537 0.0224 48.46 22.41 0.0194 42.09 19.46 83.0 52.12 0.0482 0.0252 47.97 25.01 0.0191 36.37 18.96 98.7 54.61 0.0453 0.0260 47.73 26.07 0.0219 40.18 21.94 151.4 67.96 0.0323 0.0323 47.12 32.03 0.0217 31.68 21.53 192.0 71.67 0.0283 0.0305 42.56 30.50 0.0245 34.28 24.57 251.4 77.76 0.0224 0.0326 41.67 32.41 0.0209 26.70 20.76 385

307.0 78.70 0.0213 0.0308 39.23 30.88 0.0221 28.08 22.10

16.1 45.75 0.0546 0.0319 69.32 31.71 0.0099 21.48 9.82 32.1 59.98 0.0370 0.0438 78.95 47.35 0.0121 21.77 13.06 51.0 71.54 0.0263 0.0511 77.25 55.26 0.0116 17.51 12.53 64.2 78.10 0.0203 0.0526 72.78 56.84 0.0130 17.95 14.02 101.2 82.05 0.0166 0.0530 69.75 57.23 0.0164 21.57 17.70 101.8 89.20 0.0100 0.0512 62.07 55.36 0.0116 14.02 12.50 179.4 95.74 0.0039 0.0515 58.09 55.62 0.0091 10.30 9.86 205.0 94.15 0.0054 0.0568 65.16 61.34 0.0112 12.87 12.11 245.3 94.24 0.0053 0.0571 65.44 61.67 0.0117 13.42 12.65 420

320.7 97.19 0.0026 0.0526 58.52 56.88 0.0078 8.72 8.47

Aging of a new pipe reactor

Feed: Lactic acid 0.1 mol l^-1; Pressure: 350 bar;

Temperature: 385 °C; Residence time: 100 seconds Aging time

/hours Conv.

Conc.

Lac /mol l^-1

Conc.

Ald /mol l^-1

Sel.

Ald /%

Conc.

Acr /mol l^-1

Sel.

Acr /%

1.5 74.64 0.0284 0.0310 37.08 27.68 0.0449 53.67 40.06 3.8 74.22 0.0289 0.0324 38.97 28.92 0.0458 55.06 40.87 17.3 74.44 0.0286 0.0335 40.12 29.87 0.0465 55.83 41.56 23.1 73.46 0.0297 0.0341 41.41 30.42 0.0462 56.14 41.25 24.6 73.39 0.0298 0.0332 40.38 29.64 0.0461 56.05 41.13 27.6 73.54 0.0296 0.0343 41.60 30.60 0.0463 56.23 41.35

Influence of the concentration

Pressure: 350 bar; Temperature: 385 °C; Residence time: 100 seconds;

Feed: Lactic acid Feed

Conc.

/mol l^-1

Conv.

Conc.

Lac /mol l^-1

Conc.

Ald /mol l^-1

Sel.

Ald /%

Conc.

Acr /mol l^-1

Sel.

Acr /%

0.0678 58.00 0.0285 0.0183 46.61 27.03 0.0151 38.32 22.22 0.0720 55.73 0.0337 0.0207 54.08 28.75 0.0149 38.84 20.65 0.0843 52.08 0.0404 0.0228 - 27.00 0.0292 - 34.69 1.0079 82.29 0.0431 0.0278 48.24 27.63 0.0147 25.43 14.57 0.1011 59.54 0.0409 0.0302 50.09 29.82 0.0302 50.09 29.82 0.1330 58.93 0.0546 0.0360 45.87 27.03 0.0292 37.30 21.98 0.1794 69.66 0.0420 0.0272 - 37.93 0.0184 - 25.68 0.2077 61.21 0.0403 0.0297 46.68 28.58 0.0296 46.53 28.48 0.2084 58.20 0.0436 0.0282 - 33.46 0.0315 - 30.23 0.2200 59.55 0.0445 0.0265 40.47 24.10 0.0219 33.49 19.94 0.3038 61.52 0.0390 0.0288 46.29 28.48 0.0287 46.09 28.36 0.4123 62.60 0.0386 0.0329 50.97 31.91 0.0273 42.34 26.50 0.4178 60.33 0.0504 0.0337 - 40.37 0.0195 - 23.29 0.4368 61.43 0.0421 0.0275 41.01 25.19 0.0181 27.01 16.59 0.5250 63.39 0.0384 0.0339 50.86 32.24 0.0273 41.00 25.99 0.6499 81.76 0.0296 0.0254 46.41 30.09 0.0221 16.65 13.61 1.0010 59.01 0.0410 0.0281 47.59 28.08 0.0145 24.55 14.49

Influence of the pressure

Feed: Lactic acid 0.1 mol/l; Temperature: 385 °C R.t.

/s p

/bar Conv.

Conc.

Lac /mol l^-1

Conc.

Ald /mol l^-1

Sel.

Ald /%

Conc.

Acr /mol l^-1

Sel.

Acr /%

156.6 118 82.29 0.0177 0.0262 31.97 26.31 0.0009 1.13 0.93 83.7 150 60.33 0.0396 0.0226 37.64 22.71 0.0008 1.26 0.76 98.2 200 69.66 0.0303 0.0267 38.47 26.80 0.0021 3.04 2.12 105.6 250 55.73 0.0441 0.0244 43.93 24.48 0.0044 7.95 4.43 100.3 300 59.99 0.0399 0.0261 43.67 26.20 0.0142 23.72 14.23 101.2 350 61.54 0.0383 0.0259 42.20 25.97 0.0176 28.75 17.69

Influence of the temperature

Feed: Lactic acid 0.1 mol l^-1; Pressure: 350 bar;

Residence time: 100 seconds T

/°C Conv.

Conc.

Lac /mol l^-1

Conc.

Ald /mol l^-1

Sel.

Ald /%

Conc.

Acr /mol l^-1

Sel.

Acr /%

150 0.31 0.0987 0 0 0 0 0 0

200 0.12 0.0989 0 0 0 0 0 0

250 0 0.0990 0 - 0 0 - 0

300 1.47 0.0975 0.0016 112.53 1.66 0.0010 67.39 0.99 350 22.05 0.0772 0.0134 61.26 13.51 0.0101 46.32 10.22

Screening for catalyst

Feed: Lactic acid 0.1 mol l^-1; Pressure: 350 bar Catalyst R.t.

Conv.

Conc. Lac /mol l^-1

Conc. Ald /mol l^-1

Sel. Ald /%

Y. Ald /%

Conc. Acr /mol l^-1

Sel. Acr /%

Y. Acr /%

50.4 36.54 0.0765 0.0211 47.82 17.47 0.0230 52.16 19.06 102.0 61.52 0.0464 0.0348 46.99 28.91 0.0354 47.71 29.35 -

204.0 85.41 0.0176 0.0424 41.20 35.19 0.0389 37.79 32.28

49.7 35.83 0.0680 0.0182 47.84 17.14 0.0194 51.11 18.31 99.8 66.00 0.0360 0.0296 42.25 27.88 0.0283 40.48 26.71 MgSO₄

200 ppm

214.8 91.98 0.0085 0.0433 44.46 40.89 0.0304 31.22 28.71

50.4 37.74 0.0660 0.0208 51.93 19.60 0.0199 49.66 18.74 99.5 62.28 0.0400 0.0325 49.16 30.62 0.0311 47.13 29.35 MgSO₄

800 ppm

207.7 87.80 0.0129 0.0422 45.35 39.82 0.0342 36.72 32.24

49.6 32.98 0.0710 0.0235 67.31 22.20 0.0140 39.91 13.16 97.8 72.27 0.0294 0.0454 59.21 42.79 0.0292 38.06 27.51 ZnSO₄

200 ppm

202.1 91.30 0.0092 0.0615 63.52 57.99 0.0332 34.28 31.30

50.8 44.92 0.0593 0.0318 65.69 29.51 0.0173 35.72 16.04 100.0 83.39 0.0179 0.0603 67.18 56.02 0.0226 25.20 21.01 203.7 96.82 0.0034 0.0681 65.30 63.22 0.0219 21.02 20.36 ZnSO₄

800 ppm

510.6 99.05 0.0010 0.0697 65.38 64.76 0.0128 12.01 11.90

50.4 52.18 0.0513 0.0174 31.02 16.19 0.0154 27.46 14.33 100.2 75.69 0.0261 0.0262 32.19 24.36 0.0239 29.40 22.25 KHCO₃

200 ppm

203.7 93.66 0.0068 0.0321 31.96 29.93 0.0239 23.75 22.24

50.4 27.47 0.0860 0.0122 37.41 10.28 0.0223 68.43 18.80 100.8 50.45 0.0588 0.0197 32.89 16.59 0.0349 58.25 29.39 Na₂SO₄

1000 ppm

201.3 75.52 0.0290 0.0299 33.35 25.19 0.0372 41.54 31.37

34.8 25.30 0.0792 0.0092 34.29 8.68 0.0178 66.35 16.79 99.7 45.04 0.0583 0.0130 27.33 12.31 0.0271 56.72 25.55 K₂HPO₄

3000 ppm

210.5 68.58 0.0333 0.0208 28.59 19.60 0.0262 35.99 24.68

49.5 23.38 0.0825 0.0080 31.64 7.40 0.0157 62.32 14.57 101.1 42.82 0.0616 0.0113 24.55 10.51 0.0226 49.03 21.00 203.7 65.39 0.0373 0.0209 29.70 19.42 0.0184 26.18 17.12 K₂HPO₄

5000 ppm

431.4 85.52 0.0156 0.0237 25.70 21.97 0.0030 3.28 2.80

Feed: Lactic acid 0.1 mol l^-1; Pressure: 350 bar; Temperature: 385 °C Catalyst R.t.

/s Conv.

Conc.

Lac /mol l^-1

Conc.

Ald /mol l^-1

Sel.

Ald /%

Y. Ald /%

Conc.

Acr /mol l^-1

Sel. Acr /% Y. Acr

50.4 46.07 0.0534 0.0354 77.69 35.79 0.0142 31.23 14.39 103.2 63.19 0.0364 0.0469 75.03 47.41 0.0168 26.82 16.95 -

247.2 84.26 0.0156 0.0678 81.25 68.46 0.0156 18.74 15.79

50.5 38.78 0.0606 0.0390 - 39.44 0.0142 37.09 14.39 100.7 59.99 0.0396 0.0719 - 72.58 0.0193 32.43 19.45 MgSO₄

1000 ppm

254.4 81.62 0.0182 0.1035 - 104.56 0.0208 25.76 21.02

51.9 29.91 0.0690 0.0151 51.36 15.36 0.0153 51.99 15.55 100.6 50.75 0.0485 0.0229 45.78 23.24 0.0170 34.06 17.29 Na₂SO₄

1500 ppm

203.0 67.83 0.0317 0.0353 52.86 35.85 0.0149 22.27 15.10

Various phosphate catalysts

Feed: Lactic acid 0.1 mol l^-1; Pressure: 350 bar; Residence time: 100 seconds Catalyst Conv.

Conc.

Lac /mol l

-1

Conc.

Ald /mol l^-1

Sel.

Ald /%

Conc.

Acr /mol l^-1

Sel.

Acr /%

- 56.72 0.0427 0.0287 51.26 29.07 0.0230 41.11 23.32 K₂HPO₄

1000 ppm 46.10 0.0531 0.0180 39.59 18.25 0.0206 45.41 20.93 KH₂PO₄

1000 ppm 47.33 0.0519 0.0193 41.42 19.61 0.0229 49.10 23.24 Cs₂HPO₄

1000 ppm 46.24 0.0530 0.0181 39.65 18.33 0.0208 45.67 21.12 CsH₂PO₄

1000 ppm 47.71 0.0515 0.0193 41.15 19.63 0.0223 47.38 22.61

Titration of KOH and CsOH with phosphoric acid

Feed: Lactic acid 0.1 mol l^-1 + 1500 ppm KOH;

Pressure: 350 bar; Temperature: 385 °C; Residence time: 100 seconds A =_mH₃PO₄/C_mKOH Conv.

Conc.

Lac /mol l^-1

Conc.

Ald /mol l^-1

Sel. Ald

/% Y. Ald /%

Conc.

Acr /mol l

-1

Sel. Acr

/% Y. Acr /%

0 48.11 0.0502 0.0169 36.40 17.51 0.0137 29.33 14.11 0.0001 49.20 0.0492 0.0189 39.67 19.52 0.0159 33.33 16.40 0.001 43.00 0.0552 0.0156 37.49 16.12 0.0169 40.64 17.47 0.01 43.04 0.0551 0.0155 37.31 16.06 0.0169 40.64 17.49 0.1 38.82 0.0592 0.0119 31.77 12.33 0.0182 48.56 18.85 0.33 43.86 0.0543 0.0148 34.98 15.34 0.0211 49.63 21.77 0.66 47.36 0.0509 0.0146 31.96 15.14 0.0233 50.88 24.10 1 50.47 0.0479 0.0167 34.11 17.22 0.0240 49.21 24.84 2 57.41 0.0412 0.0213 38.39 22.04 0.0232 41.69 23.94

Feed: Lactic acid 0.1 mol l^-1 +1500 ppm CsOH; Pressure: 350 bar;

Temperature: 385 °C; Residence time: 100 seconds A =

C_mH₃PO₄/C_mCsOH Conv.

(%) Conc. Lac

(mol/l) Conc. Ald

mol/l) Sel. Ald (%) Y. Ald

(%) Conc. Acr

(mol/l) Sel. Acr (mol/l) Y. Acr

(%) 0 51.47 0.0486 0.0190 36.87 18.97 0.0157 30.49 15.69 0.000145 51.12 0.0490 0.0191 37.29 19.06 0.0163 31.82 16.27 0.10015 44.34 0.0558 0.0138 31.04 13.77 0.0196 44.18 19.59 1.065 47.44 0.0527 0.0175 36.88 17.50 0.0222 46.72 22.17

Variation of KH₂PO₄ concentration

Feed: Lactic acid 0.1 mol l^-1; Pressure: 350 bar KH₂PO₄

Conc.

/ppm T

/°C Conv.

Conc.

Lac /mol l^-1

Conc.

Ald /mol l^-1

Sel.

Ald /%

Conc.

Acr /mol l^-1

Sel.

Acr /%

0 350 23.77 0.0759 0.0129 54.55 12.97 0.0110 46.56 11.07 50 350 20.01 0.0797 0.0107 53.45 10.70 0.0108 54.35 10.88 200 350 18.89 0.0808 0.0122 - 12.30 0.0114 - 11.41 1000 350 15.76 0.0839 0.0059 37.49 5.91 0.0101 64.15 10.11 2000 350 16.36 0.0833 0.0057 34.90 5.71 0.0103 63.45 10.38

0 385 56.36 0.0435 0.0296 52.70 29.70 0.0239 42.53 23.97 50 385 51.64 0.0482 0.0230 44.63 23.05 0.0258 50.16 25.90 200 385 49.29 0.0505 0.0206 42.00 20.70 0.0245 49.88 24.59 1000 385 47.03 0.0528 0.0199 42.40 19.94 0.0225 48.05 22.60 2000 385 47.13 0.0527 0.0194 41.43 19.53 0.0215 45.78 21.58

0 420 85.16 0.0148 0.0588 69.27 58.99 0.0154 18.19 15.49 50 420 82.82 0.0171 0.0574 69.62 57.66 0.0166 20.11 16.66 200 420 81.63 0.0183 0.0561 69.04 56.36 0.0156 19.17 15.65 1000 420 83.21 0.0167 0.0563 67.94 56.53 0.0146 17.60 14.64 2000 420 83.21 0.0167 0.0545 65.73 54.69 0.0142 17.11 14.23

Stability of acrylic acid

Variation of temperature and residence time

* quantification using the same response factor for lactic acid and 3-hydroxypropionic acid

Influence of KH₂PO₄

Feed: Acrylic acid 0.1 mol l^-1; Pressure: 350 bar;

Temperature: 385 °C Catalyst R.t.

Conc.

Lac+Hpa*

/mol l^-1 Conv.

Conc.

Acr /mol l^-1

Sel.

Lac /%

49.2 0.0092 41.43 0.0728 13.64 6.54 100.7 0.0059 67.43 0.0397 5.84 4.18 148.7 0.0039 80.25 0.0237 3.37 2.80 KH₂PO₄

5000 pppm

203.3 0.0029 86.76 0.0156 2.33 2.07

- 100.5 0.0093 19.17 0.0998 26.46 6.90

* quantification using the same response factor for lactic acid and 3-hydroxypropionic acid Feed: Acrylic acid 0.05 mol l^-1; Pressure: 350 bar

R.t.

/s T /°C

Conv.

Conc.

Acr /mol l^-1

Conc.

Lac+Hpa*

/mol l^-1 100.2 350 15.91 0.0422 0.0043 153.7 350 19.11 0.0406 0.0048 206.2 350 22.61 0.0388 0.0052 304.2 350 28.22 0.0360 0.0057

50.2 385 15.33 0.0425 0.0029 101.3 385 20.92 0.0397 0.0034 149.9 385 26.68 0.0368 0.0036 199.4 385 33.00 0.0336 0.0036 320.9 385 38.77 0.0307 0.0035

22.6 420 15.66 0.0423 0.0036 50.0 420 21.99 0.0391 0.0037 105.6 420 28.09 0.0361 0.0032 160.9 420 33.99 0.0331 0.0025 219.4 420 38.74 0.0307 0.0023 344.7 420 47.09 0.0265 0.0020

Feed: Acrylic acid 0.05 mol l^-1; Pressure: 350 bar; 200 ppm KH₂PO₄ R.t.

/s T

/°C Conv /%

Conc.

Acr /mol l^-1

Conc.

Lac+Hpa*

/mol l^-1 20.5 350 8.65 0.0459 0.0030 40.9 350 15.06 0.0427 0.0042 80.4 350 25.18 0.0376 0.0051 150.8 350 28.09 0.0362 0.0065 201.7 350 30.20 0.0351 0.0069 508.4 350 47.37 0.0265 0.0069

25.6 385 16.22 0.0421 0.0037 38.9 385 20.93 0.0398 0.0042 103.2 385 32.70 0.0338 0.0046 156.0 385 37.19 0.0316 0.0045 204.2 385 43.45 0.0284 0.0044 365.2 385 60.99 0.0196 0.0037

25.5 420 14.94 0.0428 0.0031 50.9 420 19.15 0.0407 0.0031 106.1 420 34.39 0.0330 0.0027 159.8 420 40.20 0.0301 0.0025 207.8 420 51.27 0.0245 0.0022 312.8 420 61.69 0.0193 0.0019

* quantification using the same response factor for lactic acid and 3-hydroxypropionic acid

Reactants with similar structure to lactic acid

Feed: Methyl lactate 0.1 mol l^-1; Pressure: 350 bar T /°C R.t.

/s Conv.

Conc.

Lac /mol l^-1

Conc.

LacMe /mol l^-1

Conc.

Ald /mol l^-1

Sel.

Ald /%

Conc.

Acr /mol l^-1

Sel. Acr /%

Acr /%

31.6 9.63 0.0789 0.0117 0.0062 63.84 6.15 0.0037 38.24 3.68 69.8 20.04 0.0757 0.0045 0.0108 53.72 10.77 0.0077 38.22 7.66 150.8 36.83 0.0633 0 0.0161 43.59 16.06 0.0132 35.65 13.13 350

227.2 44.58 0.0555 0 0.0179 40.13 17.89 0.0152 33.95 15.13

35.8 33.63 0.0575 0.0090 0.0160 47.51 15.98 0.0115 34.05 11.45 74.3 55.81 0.0443 0 0.0240 42.93 23.96 0.0181 32.38 18.07 146.3 69.51 0.0306 0 0.0292 41.86 29.10 0.0210 30.15 20.96 385

228.2 77.64 0.0224 0 0.0297 38.14 29.61 0.0207 26.56 20.62

Feed: 2-hydroxy-isobutyric acid 0.1 mol l^-1; Pressure: 350 bar; Temperature 385 °C R.t.

/s Conv.

Conc.

Hba /mol l^-1

Conc. Maa /mol l^-1 50 93.19 0.0068 0.0881 100 92.69 0.0073 0.0799 200 93.29 0.0067 0.0702

Feed: Methacrylic acid 0.1 mol l^-1; Pressure: 350 bar; Temperature 385 °C R.t.

/s Conv.

Conc.

Maa /mol l^-1

Conc.

Hba*

/mol l^-1 50 12.01 0.0441 0.0028 100 17.19 0.0415 0.0033 200 25.25 0.0375 0.0031

*isomery has been neglected in HPLC analysis

Feed: 2-hydroxy-3-methylbutyric acid 0.1 mol l^-1; Pressure: 350 bar; Temperature 385 °C R.t.

/s Conv.

/% Conc. Hmb

/mol l^-1 Conc. Mba /mol l^-1

50 92.19 0.0079 0.0005

100 88.76 0.0113 0

200 86.63 0.0135 0

Feed: 2-methyl-3-butenoic acid 0.1 mol l^-1; Pressure: 350 bar; Temperature 385 °C R.t.

/s Conv.

/% Conc. Hmb*

/mol l^-1 Conc. Mba /mol l^-1 50 93.70 0.0066 0.0032 100 98.89 0.0102 0.0006 200 99.04 0.0116 0.0005

*isomery has been neglected in HPLC analysis

Feed: 2-Methoxypropionic acid 0.1 mol l^-1; Pressure: 350 bar; Temperature: 385 °C R.t.

/s Conv.

Conc.

Lac /mol l^-1

Conc.

Ald /mol l^-1

Sel.

Ald /%

Conc.

Acr /mol l^-1

Sel. Acr /%

Acr /%

50 41.70 0.0585 0.0203 48.52 20.23 0.0149 35.61 14.85 100 65.74 0.0344 0.0326 49.44 32.50 0.0232 35.17 23.12 200 84.92 0.0151 0.0427 50.15 42.58 0.0267 31.38 26.64

Feed: Lactic acid 0.1 mol l^-1; Pressure: 350 bar; Temperature: 385 °C R.t.

/s Conv.

Conc.

Lac /mol l^-1

Conc.

Ald /mol l^-1

Sel.

Ald /%

Conc.

Acr /mol l^-1

Sel. Acr /%

Acr /%

50 34.11 0.0653 0.0190 56.32 19.21 0.0159 47.02 16.04 100 58.53 0.0411 0.0300 51.74 30.28 0.0253 43.58 25.51 200 82.42 0.0174 0.0402 49.21 40.56 0.0290 35.48 29.24

Feed: 3-hydroxypropionic acid (Hpa) 0.1 mol l^-1; Pressure: 350 bar; Temperature: 385 °C R.t.

Conv.

Conc.

Hpa /mol l^-1

Conc.

Ald*

/mol l^-1

Sel.

Ald*

Conc.

Acr /mol l^-1

Sel. Acr /%

Acr /%

49.9 34.11 0.0126 0.0026 3.00 2.6218 0.0472 53.98 47.18 102.1 58.53 0.0178 0.0015 1.88 1.5471 0.0586 71.31 58.60

206.6 82.42 0.0257 0 0 0 0.0605 81.38 60.46

* ”Ald”- can not be acetaldehyde as shown by ¹H-NMR analysis; there is a peak, however, corresponding to the retention time of acetaldehyde.

Feed: Methyl lactate 0.1 mol l^-1; Pressure: 350 bar;

Temperature: 385 °C; Residence time: 100 seconds Conc.

KOH /ppm

Conv.

Conc. Lac /mol l^-1

Conc.

Ald /mol l^-1

Sel.

Ald /%

Y. Ald /%

Conc. Acr /mol l^-1

Sel.

Acr /%

500 61.55 0.0430 0.0153 30.69 16.50 0.0115 23.01 12.37 1000 62.29 0.0423 0.0172 33.92 18.48 0.0089 17.67 9.63

Influence of acids Acetic acid

Feed: Lactic acid 0.1 mol l^-1; Pressure: 350 bar; Temperature: 385 °C;

Residence time: 100 seconds Conc.

AcOH / mol l^-1

Conv.

Conc.

Lac / mol l^-1

Conc.

Ald / mol l^-1

Sel.

Ald /%

Conc.

Acr /mol l^-1

Sel.

Acr /%

0.01 60.17 0.0397 0.0244 40.69 24.48 0.0195 32.56 19.59 0.03 59.95 0.0399 0.0267 44.66 26.77 0.0198 33.04 19.81 0.07 60.02 0.0399 0.0269 44.88 26.94 0.0201 33.56 20.14 0.18 61.43 0.0385 0.0327 53.40 32.80 0.0198 32.32 19.85

Phosphoric acid

Feed: Lactic acid 0.1 mol l^-1; Pressure: 350 bar; Residence time: 100 seconds T

/°C

Conc.

H₃PO₄ /mol l^-1

Conv.

Conc.

Lac / mol l^-1

Conc.

Ald / mol l^-1

Sel.

Ald /%

Conc.

Acr /mol l^-1

Sel.

Acr /%

350 0.14 54.13 0.0450 0.0447 84.16 45.55 0.0054 10.11 5.47 385 0.01 63.20 0.0361 0.0401 64.68 40.88 0.0179 28.86 18.24 385 0.03 71.69 0.0278 0.0498 70.80 50.76 0.0143 20.26 14.52 385 0.07 81.49 0.0182 0.0638 79.67 64.92 0.0100 12.48 10.17 385 0.14 86.12 0.0136 0.0708 83.67 72.06 0.0080 9.41 8.11

Influence of bases

Feed: Lactic acid 0.1 mol l^-1; Pressure: 350 bar;

Temperature: 385 °C; Residence time: 100 seconds Conc.

LiOH /ppm

Conv.

Conc.

Lac / mol l^-1

Conc.

Ald / mol l^-1

Sel.

Ald /%

Conc.

Acr /mol l^-1

Sel.

Acr /%

100 61.28 0.0388 0.0121 19.76 12.11 0.0148 24.09 14.76 500 57.46 0.0426 0.0168 29.16 16.76 0.0095 16.48 9.47 1000 53.40 0.0467 0.0168 31.39 16.76 0.0055 10.24 5.47 Conc.KOH

/ppm

Conv.

Conc.

Lac / mol l^-1

Conc.

Ald / mol l^-1

Sel.

Ald /%

Conc.

Acr /mol l^-1

Sel.

Acr /%

100 53.40 0.0467 0.0130 24.33 13.00 0.0165 30.89 16.50 500 58.91 0.0412 0.0166 28.13 16.58 0.0134 22.69 13.37 1000 58.23 0.0418 0.0167 28.66 16.69 0.0109 18.72 10.90 Conc.

CsOH /ppm

Conv.

Conc.

Lac / mol l^-1

Conc.

Ald / mol l^-1

Sel.

Ald /%

Conc.

Acr /mol l^-1

Sel.

Acr /%

100 57.47 0.0426 0.0206 35.85 20.60 0.0168 29.15 16.75 500 58.45 0.0416 0.0162 27.69 16.19 0.0157 26.78 15.65 1000 56.58 0.0435 0.0151 26.64 15.08 0.0141 24.93 14.11

Gas phase analysis

Feed: Lactic acid 0.1 mol l^-1; Pressure: 350 bar T

/°C R.t.

/s CO

/% mol CO₂

/% mol C₂H₄

/% mol CO/CO₂ Ratio 350 50 0.8589 0.0728 0.0132 11.80 350 50 0.8272 0.0654 0.0106 12.65 350 100 0.8219 0.0701 0.0258 11.72 350 200 0.8568 0.1073 0.0447 7.99 385 50 0.8527 0.0741 0.0294 11.51 385 100 0.7774 0.1001 0.0559 7.77 385 200 0.6755 0.1623 0.0873 4.16 420 50 0.8342 0.0657 0.0121 12.70 420 100 0.7338 0.0996 0.0185 7.37 420 200 0.6435 0.1296 0.0250 4.97

Feed: Acetaldehyde 0.05 mol l^-1; Pressure: 350 bar T

/°C R.t.

/s CO

/% mol CO₂

/% mol C₂H₄

/% mol CO/CO₂ Ratio 425 150 0.3735 0.0207 0.0003 18.04

1H-NMR Analysis of the Lactic acid/3-hydroxypropionic acid molar ratio and regressions used to determine the concentrations of the two isomers

Feed: Lactic acid 0.1 mol l^-1;

Pressure: 350 bar Feed: Acrylic acid 0.05 mol l^-1; Pressure: 350 bar T

/°C R.t.

/s Lac/Hpa molar ratio T /°C R.t. /s Lac/Hpa molar ratio

25 - 25 0.09

50 - 50 0.16

100 -

350

100 0.28

350

890 9.52

25 0.24

65 66.67 80 0.59

80 33.33 100 0.69

385

150 22.22

385

150 0.74

50 66.67 25 0.10

100 33.33 80 0.29

420

200 13.33

420

200 0.27

Feed: Lactic acid 0.1 mol l^-1; Pressure: 350 bar;

200 ppm KH₂PO₄

Feed: Acrylic acid 0.05 mol l^-1; Pressure: 350 bar;

200 ppm KH₂PO₄ T

/°C R.t.

/s Lac/Hpa molar ratio T

/°C R.t.

/s Lac/Hpa molar ratio

25 133.33 20 0.11

150 13.33 200 0.36

350

300 5.56

350

500 0.55

16.5 296.30 25 0.23

150 22.22 150 0.60

385

350 9.52

385

350 0.78

50 66.67 25 0.19

100 33.33 150 0.31

420

200 13.33

420

300 0.32

Feed Catalyst /g g^-1

Temp.

/°C Regression: Lac/Hpa molar ratio at residence time ττττ Lac 0.1 M 200 ppm

KH2PO4

385 7008.9·τ^-1.1351

Acr 0.05 M 200 ppm

KH₂PO₄ 350 -2·10^-6·τ²+0.0017·τ+0.0806 Acr 0.05 M 200 ppm

KH₂PO₄ 385 0.2072·ln(τ)-0.4402

Acr 0.05 M 200 ppm

KH₂PO₄ 420 -3·10^-6·τ²+0.0015·τ+0.1535

Acr 0.05 M - 385 0.2833·ln(τ)-0.668

Acr 0.05 M - 420

-5 3 2

9.26 10 0.6346 1.571 1.0295

9.26 10 0.1582 1.527 0.867

τ τ τ

⋅ ⋅ + ⋅ + ⋅ +

Data used for the simulation

Concentrations are given in mol/l and are calculated at the conditions from reactor; “-1” as a concentration refers to concentrations which are not to be taken into account by the software

Data from experiments without catalyst

R.t. /s Lac /mol l^-1

Ald /mol l^-1

Acr /mol l^-1

D /mol l^-1

Acr1 /mol l^-1

Hpa1 /mol l^-1

D1 /mol l^-1

0 0.0663 0 0 0 0.0330 0 0

18.0 0.0635 0.0023 0.0014 -1 -1 -1 -1 25.6 -1 -1 -1 -1 0.0297 0.0011 0.0023 32.2 0.0612 0.0035 0.0026 -1 -1 -1 -1 50.0 0.0579 0.0049 0.0038 -1 -1 -1 -1 51.2 -1 -1 -1 -1 0.0279 0.0017 0.0034 65.3 0.0564 0.0057 0.0048 -1 -1 -1 -1 100.1 0.0515 0.0076 0.0074 -1 -1 -1 -1 100.2 -1 -1 -1 -1 0.0278 0.0028 0.0024 101.2 0.0505 0.0082 0.0069 0.0007 -1 -1 -1 150.8 0.0464 0.0099 0.0083 0.0016 -1 -1 -1 153.7 -1 -1 -1 -1 0.0267 0.0032 0.0032 190.5 0.0443 0.0092 0.0106 0.0021 -1 -1 -1 206.2 -1 -1 -1 -1 0.0256 0.0034 0.0040 253.5 0.0398 0.0131 0.0104 0.0030 -1 -1 -1 304.2 -1 -1 -1 -1 0.0237 0.0038 0.0055 350 °C

305.7 0.0392 0.0111 0.0124 0.0036 -1 -1 -1

R.t. /s Lac

/mol l^-1 Ald

/mol l^-1 Acr /mol l^-1 D

/mol l^-1 Acr1

/mol l^-1 Hpa1 /mol l^-1 Lac1

/mol l^-1 D1 /mol l^-1

0 0.0509 0 0 0 0.0276 0 0 0

16.6 0.0462 0.0051 0.0042 -1 -1 -1 -1 -1 20.2 0.0426 0.0065 0.0050 -1 -1 -1 -1 -1 31.9 0.0393 0.0083 0.0069 -1 -1 -1 -1 -1 50.2 -1 -1 -1 -1 0.0234 0.0011 0.0005 0.0026 64.6 0.0297 0.0130 0.0107 -1 -1 -1 -1 -1

83.0 0.0265 0.0139 0.0105 0 -1 -1 -1 -1

98.7 0.0250 0.0151 0.0121 -1 -1 -1 -1 -1 101.3 -1 -1 -1 -1 0.0218 0.0012 0.0007 0.0039 149.9 -1 -1 -1 -1 0.0202 0.0011 0.0008 0.0054 151.4 0.0178 0.0177 0.0119 0.0035 -1 -1 -1 -1 192.0 0.0156 0.0176 0.0135 0.0043 -1 -1 -1 -1 199.4 -1 -1 -1 -1 0.0185 0.0011 0.0009 0.0071 251.4 0.0123 0.0180 0.0115 0.0091 -1 -1 -1 -1 307.0 0.0117 0.0175 0.0121 0.0096 -1 -1 -1 -1 385 °C

320.9 -1 -1 -1 -1 0.0169 0.0010 0.0009 0.0088

R.t. /s Lac

/mol l^-1 Ald

/mol l^-1 Acr /mol l^-1 D

/mol l^-1 Acr1

/mol l^-1 Hpa1 /mol l^-1 Lac1

/mol l^-1 D1 /mol l^-1

0 0.0300 0 0 0 0.0163 0 0 0

16.1 0.0176 0.0111 0.0032 -1 -1 -1 -1 -1 22.6 -1 -1 -1 -1 0.0137 0.0010 0.0001 0.0014 32.1 0.0120 0.0142 0.0039 -1 -1 -1 -1 -1 50.0 -1 -1 -1 -1 0.0127 0.0010 0.0002 0.0024 51.0 0.0085 0.0166 0.0038 0.0035 -1 -1 -1 -1 64.2 0.0066 0.0171 0.0042 0.0022 -1 -1 -1 -1 101.2 0.0054 0.0172 0.0053 0.0044 -1 -1 -1 -1 101.8 0.0032 0.0166 0.0038 0.0064 -1 -1 -1 -1 105.6 -1 -1 -1 -1 0.0117 0.0008 0.0002 0.0035 160.9 -1 -1 -1 -1 0.0107 0.0006 0.0002 0.0047 179.4 0.0013 0.0167 0.0030 0.0091 -1 -1 -1 -1 205.0 0.0018 0.0184 0.0036 0.0081 -1 -1 -1 -1 219.4 -1 -1 -1 -1 0.0100 0.0006 0.0002 0.0055 245.3 0.0017 0.0185 0.0038 0.0079 -1 -1 -1 -1 320.7 0.0008 0.0171 0.0025 0.0096 -1 -1 -1 -1 420 °C

344.7 -1 -1 -1 -1 0.0086 0.0005 0.0001 0.0070

Data from experiments with 200 ppm KH₂PO₄

R.t. /s Lac

/mol l^-1 Ald

/mol l^-1 Acr /mol l^-1 D

/mol l^-1 Acr1

/mol l^-1 Hpa1 /mol l^-1 Lac1

/mol l^-1 D1 /mol l^-1

0 0.0660 0 0 0 0.0331 0 0 0

20.2 0.0611 0.0025 0.0019 0.0002 -1 -1 -1 -1 20.5 -1 -1 -1 -1 0.0303 0.0018 0.0002 0.0009 25.4 0.0599 0.0024 0.0022 0.0012 -1 -1 -1 -1 40.9 -1 -1 -1 -1 0.0282 0.0024 0.0004 0.0022 50.7 0.0555 0.0032 0.0043 0.0026 -1 -1 -1 -1 80.3 0.0524 0.0042 0.0060 0.0029 -1 -1 -1 -1 80.4 -1 -1 -1 -1 0.0248 0.0028 0.0006 0.0050 102.3 0.0487 0.0051 0.0074 0.0042 -1 -1 -1 -1 150.8 -1 -1 -1 -1 0.0238 0.0033 0.0010 0.0050 152.9 0.0447 0.0054 0.0092 0.0058 -1 -1 -1 -1 155.5 0.0441 0.0061 0.0093 0.0056 -1 -1 -1 -1 201.7 -1 -1 -1 -1 0.0231 0.0034 0.0012 0.0054 205.0 0.0404 0.0066 0.0108 0.0071 -1 -1 -1 -1 508.4 -1 -1 -1 -1 0.0174 0.0032 0.0014 0.0112 350 °C

609.4 0.0258 0.0076 0.0148 0.0155 -1 -1 -1 -1

R.t. /s Lac

/mol l^-1 Ald

/mol l^-1 Acr

/mol l^-1 Hpa /mol l^-1 D

/mol l^-1 Acr1

/mol l^-1 Hpa1

/mol l^-1 Lac1

/mol l^-1 Ald1

/mol l^-1 D1 /mol l^-1

0 0.0550 0 0 0 0 0.0277 0 0 0 0

16.8 0.0432 0.0040 0.0047 0.0002 0.0029 -1 -1 -1 -1 -1 25.6 -1 -1 -1 -1 -1 0.0232 0.0017 0.0004 0.0003 0.0021 38.9 -1 -1 -1 -1 -1 0.0219 0.0018 0.0006 0.0002 0.0032 50.9 0.0315 0.0081 0.0096 0.0004 0.0054 -1 -1 -1 -1 -1 81.7 0.0251 0.0104 0.0119 0.0005 0.0071 -1 -1 -1 -1 -1 103.2 -1 -1 -1 -1 -1 0.0186 0.0017 0.0009 0.0005 0.0060 103.5 0.0216 0.0108 0.0132 0.0006 0.0087 -1 -1 -1 -1 -1 154.0 0.0165 0.0119 0.0142 0.0007 0.0117 -1 -1 -1 -1 -1 156.0 -1 -1 -1 -1 -1 0.0174 0.0016 0.0009 0.0006 0.0072 186.0 0.0147 0.0139 0.0144 0.0008 0.0113 -1 -1 -1 -1 -1 197.4 0.0143 0.0135 0.0144 0.0008 0.0120 -1 -1 -1 -1 -1 204.2 -1 -1 -1 -1 -1 0.0157 0.0015 0.0010 0.0008 0.0089 361.6 0.0082 0.0127 0.0136 0.0009 0.0195 -1 -1 -1 -1 -1 385 °C

365.2 -1 -1 -1 -1 -1 0.0108 0.0011 0.0009 0.0011 0.0138

R.t. /s Lac

/mol l^-1 Ald

/mol l^-1 Acr

/mol l^-1 Hpa /mol l^-1 D

/mol l^-1 Acr1

/mol l^-1 Hpa1

/mol l^-1 Lac1

/mol l^-1 Ald1

/mol l^-1 D1 /mol l^-1

0 0.0325 0 0 0 0 0.0164 0 0 0 0

10.0 0.0199 0.0066 0.0033 0 0.0027 -1 -1 -1 -1 -1

25.5 -1 -1 -1 -1 -1 0.0139 0.0008 0.0002 0.0002 0.0012 25.8 0.0126 0.0123 0.0041 0.0001 0.0034 -1 -1 -1 -1 -1 50.8 0.0093 0.0149 0.0041 0.0002 0.0040 -1 -1 -1 -1 -1 50.9 -1 -1 -1 -1 -1 0.0132 0.0008 0.0002 0.0003 0.0018 81.4 0.0056 0.0178 0.0046 0.0002 0.0043 -1 -1 -1 -1 -1 102.2 0.0038 0.0183 0.0056 0.0002 0.0047 -1 -1 -1 -1 -1 106.1 -1 -1 -1 -1 -1 0.0107 0.0007 0.0002 0.0006 0.0042 129.4 0.0029 0.0188 0.0051 0.0002 0.0055 -1 -1 -1 -1 -1 153.9 0.0025 0.0177 0.0050 0.0002 0.0071 -1 -1 -1 -1 -1 159.8 -1 -1 -1 -1 -1 0.0098 0.0006 0.0002 0.0006 0.0051 207.8 -1 -1 -1 -1 -1 0.0080 0.0005 0.0002 0.0008 0.0069 208.8 0.0022 0.0197 0.0042 0.0003 0.0061 -1 -1 -1 -1 -1 312.8 -1 -1 -1 -1 -1 0.0063 0.0005 0.0002 0.0009 0.0086 420 °C

313.9 0.0014 0.0176 0.0037 0.0003 0.0096 -1 -1 -1 -1 -1

1H-NMR Data of the reactor samples

The spectra have been acquired using a Bruker DRX-500 spectrometer. The samples consisted of aqueous solutions to which D₂O has been added. The chemical shift, δ, is given in ppm and is relative to the tetramethylsilane (TMS) internal standard. In brackets, the number of signals (singlet, dublet, triplet, etc.), the number of protons involved as well as an identification label are given in this order. The spin-spin coupling constant, J, is given in Hz with a superscript indicating the number of bonds separating the nuclei. All measurements were carried out at room temperature with a resolution of 500 MHz.

Acetaldehyde: ¹H-NMR (500 MHz, H2O/D2O, TMS): δ = 2.166 (d, 3H, 2H), 9.600 (q, 1H, 1H) ppm; ³J_1H,2H= 3.0 Hz.

Lactic acid: ¹H-NMR (500 MHz, H₂O/D₂O, TMS): δ = 1.345 (d, 1H, 2H), 4.310 (q, 1H, 1H) ppm; ³J_1H,2H= 7.0 Hz.

Acrylic acid: ¹H-NMR (500 MHz, H2O/D2O, TMS): δ = 5.920 (dd, 1H, 2Hcis), 6.105 (dd, 1H, 1H), 6.335 (dd, 1H, 2Htrans) ppm; ³J_1H,2Hcis= 10.5 Hz; ²J2H,2Hgeminal= 0.75 Hz;

3J_1H,2Htrans= 17.5 Hz .

3-Hydroxypropionic acid: ¹H-NMR (500 MHz, H2O/D2O, TMS): δ = 2.544 (t, 2H, 1H), 3.785 (t, 2H, 2H) ppm; ³J_1H,2H= 6.0 Hz.

2-Methoxypropionic acid: ¹H-NMR (500 MHz, H2O/D2O, TMS): δ = 1.292 (d, 3H, 1H), 3.285 (s, 3H, 3H), 3.943 (q, 1H, 2H) ppm; ³J_1H,2H= 7.0 Hz.

Acetic acid: ¹H-NMR (500 MHz, H2O/D2O, TMS): δ = 2.080 (s, 3H, 1H) ppm.

Ethylene gylcol: ¹H-NMR (500 MHz, H2O/D2O, TMS): δ = 3.598 (s, 4H, 1H) ppm.

Chemical substances used in experiments

Substance CAS No. Concentration /% Manufacturer

Acetaldehyde 75-07-0 99.5 Acros

Acetic acid 64-19-7 99.8 Acros

Acrylic acid 79-10-7 99 BASF

DL-2-bromopropionic acid 598-72-1 99+ Acros

Cesium hydroxide, monohydrate 35103-79-8 99.5 Acros

Ethyl acetate 141-78-6 99.5+ Acros

2-hydroxyisobutyric acid 594-61-6 98 Acros

3-hydroxypropionic acid 503-66-2 30 TCI

(S)-(+)-2-hydroxy-

3-methylbutanoic acid 17407-55-5 99+ Acros

DL-Lactic acid 50-21-5 85 Acros

Lactic acid, lithium salt 867-55-0 99 Acros

Lithium hydroxide 1310-65-2 98 Merck

Methanol 67-56-1 99+ Acros

Magnesium sulfate, anhydrous 7487-88-9 97 Acros

3-methyl-2-butenoic acid 541-47-9 97 Sigma-Aldrich

Methyl-(S)-(-)-lactate 27871-49-4 97 Acros

Phosphoric acid 7664-38-2 85 Acros

Potassium hydroxide 1310-58-3 85 Acros

Potassium hydrogen carbonate 298-14-6 99 Merck

Potassium phosphate, dibasic,

anhydrous 7758-11-4 99 Acros

Potassium phosphate, monobasic 7778-77-0 99 Acros

Propionic acid 79-09-4 99 Aldrich

Sodium hydroxide 1310-73-2 99 Merck

Sodium methoxide 124-41-4 99 Acros

Sodium sulfate, anhydrous 7757-82-6 99 Acros

Sulfuric acid 7664-93-9 for standard

0.5 M solution Merck

Zinc sulfate, heptahydrate 7446-20-0 99 Merck

Zusammenfassung

Acrylsäure findet eine Anwendung in der chemischen Industrie als Zwischenprodukt für die Synthese von Polyacrylaten und Kopolymeren, die in der Formulierung von Farbstoffen, Lacken usw. angewendet werden. Industriell wird Acrylsäure aus Naphta über Propen hergestellt und ist dadurch von der Erdöl- und Erdgasknappheit betroffen.

Eine Möglichkeit für die Herstellung von Acrylsäure aus nachwachsenden Rohstoffen ist die Nutzung von Milchsäure und deren Dehydratisierung in nah- und überkritischem Wasser.

Überkritisches Wasser ist ein sauberes, umweltschonendes Reaktionsmedium. Milchsäure kann aus Kohlenhydraten gewonnen werden und steht damit in großen Mengen zur Verfügung, findet allerdings noch wenige industrielle Anwendungen.

Versuche Milchsäurederivate zu Acrylsäurederivaten umzusetzen existieren schon seit ungefähr 70 Jahren. Dennoch hat dieser synthetische Weg bis dato keine industrielle Anwendung gefunden.

Im Rahmen dieser Arbeit wurden Experimente entworfen und durchgeführt, die dem Zweck dienten, die Reaktion zur Herstellung von Acrylsäure näher zu bringen. Insofern wurden die Reaktionskinetik und der Reaktionsmechanismus untersucht, um optimale

Reaktionsbedingungen zu finden.

Eine Versuchsanlage für die Durchführung der Experimente im überkritischen Wasser wurde aufgebaut und eine passende Methode für die Quantifizierung der im Reaktionsgemisch anwesenden Substanzen sowohl in der Flüssigphase als auch in der Gasphase entwickelt.

Um optimale Reaktionsbedingungen zu finden, wurde der Einfluss von unterschiedlichen Parametern wie Temperatur, Druck, Konzentration des Eduktes und Verweilzeit auf die Reaktion untersucht. Des Weiteren wurde der Einfluss der Zugabe von Säuren, Basen und Salzen untersucht. Ein Optimum für die Reaktion wurde bei 385 °C, 350 bar und 200 Sekunden Verweilzeit gefunden. Bei denselben Bedingungen sinkt die Selektivität zu

Acetaldehyd (dem wichtigsten Nebenprodukt der Reaktion) um 5 bis 6 %, wenn eine Menge von 200 ppm (g g^-1) Kaliumdihydrogenphosphat in der Eduktlösung anwesend ist.

Die Stabilität von Acrylsäure in nah- und überkritischem Wasser wurde untersucht. Es wurde festgestellt, dass die Addition von Wasser zu Acrylsäure nicht nur zu 3-Hydroxypropionsäure, dem normalen Produkt einer Markovnikov-Addition, führt, sondern auch zu Milchsäure, insbesondere bei 390 °C, wo sich das Stoffmengenverhältnis von Milch- zu

3-Hydroxypropionsäure einem Wert von eins nähert.

Ein bislang ungeklärtes Problem bei der Aufklärung des Reaktionsmechanismus betrifft die Decarboxylierung von Milchsäure. Es kann zwar Kohlendioxid detektiert werden, aber das erwartete Decarboxylierungsprodukt Ethanol ist im Reaktionsgemisch unter keinen

Bedingungen zu finden. Stattdessen findet man nur Acetaldehyd. Demzufolge wurde in der Fachliteratur postuliert, dass die Decarboxylierung von Milchsäure eine radikalische Reaktion ist. In dieser Arbeit wurde gezeigt, dass die Decarboxylierung von Milchsäure nicht stattfindet und die größten Mengen von Kohlendioxid durch die Wassergas-Shift-Reaktion aus

Kohlenmonoxid entstehen.

Ein kinetisches Modell basierend auf den experimentellen Daten wurde entwickelt. Die Geschwindigkeitskonstanten für die Reaktionen, in denen Acetaldehyd, Acryl-, Milch- und 3-Hydroxypropionsäure beteiligt sind, wurden mit Hilfe einer Simulationssoftware für drei Temperaturen (350, 385 und 420 °C) ermittelt.

Horea Szedlacsek Am Pelz 82 64295 Darmstadt

e-mail: horea.szedlacsek@googlemail.com

Darmstadt, 07.11.2012

Erklärung

Ich erkläre hiermit, dass ich meine Dissertation selbstständig und nur mit den angegebenen Hilfsmitteln angefertigt habe.

(Horea Szedlacsek)

Horea Szedlacsek Am Pelz 82 64295 Darmstadt

e-mail: horea.szedlacsek@googlemail.com

Darmstadt, 07.11.2012

Erklärung

Ich erkläre hiermit, noch keinen Promotionsversuch unternommen zu haben.

(Horea Szedlacsek)

Im Dokument On the dehydration of lactic acid in near- and supercritical water (Seite 113-140)